The following U.S. Patents are incorporated herein by reference:
U.S. Pat. No. 5,967,866 discloses a lower unit for a marine propulsion system having a flow disrupter positioned along the side wall of the vertical strut above the torpedo gearcase. The strut has a high pressure side and low pressure side which results from the strut being positioned at an angle with respect to the direction of boat travel in order to compensate for steering torque. The flow disrupter is positioned on the low pressure side of the strut, and promotes the separation of water passing over the vertical strut in a controlled manner, thereby reducing steering jerks during acceleration due to dramatic hydrodynamic flow changes. The flow disrupter consists of a series of steps or textured areas positioned along the aft section of the vertical strut. In a preferred embodiment, each of the steps contains a vent passage permitting exhaust to exit the strut through the steps to further promote controlled separation of water passing over the strut.
U.S. Pat. No. 5,277,634 discloses a lower unit for a marine propulsion device, such as an outboard motor or a stern drive unit.
U.S. Pat. No. 4,447,214 discloses a lower unit having a gearcase normally submerged in water and arranged to discharge engine exhaust gas rearwardly from the rear end into the water exteriorly of the propeller hub. A ring member or thrust ring including a hub mounted on the propeller shaft for common therewith, an annular collar and a plurality of circumferentially-spaced, radially extending spokes or ribs interconnecting the annular collar and the hub serves as a fishline and weed cutter. The annular collar includes an annular outer surface which extends closely adjacent an annular inner surface in the interior of the gearcase adjacent the trailing edge of the gearcase. In one embodiment, forward migration of the engine exhaust gases along the outer surface of the gearcase, which can cause unstable handling of the lower unit, is prevented by an anti-ventilation means including an annular section on the ring member collar located rearwardly of the annular outer surface and rearwardly of the trailing edge of the gearcase and having an outer surface tapering radially outwardly from the outer surface of the gearcase toward the propeller.
U.S. Pat. No. 4,295,835 discloses an engine driven outboard drive unit for propelling a watercraft having a vertical drive shaft driving a horizontal propeller shaft on which a propeller is mounted. The drive unit has a gearcase torpedo which houses both the propeller shaft and an annular exhaust gas passage. The exhaust passage discharges aft through the plane of the propeller. A small annular projection is formed around the aft end of the torpedo to improve high speed performance.